1. Field of the Invention
The present invention is directed to a non-contact electrical power transmission system, and more particularly to a system of transmitting an electric power from a high frequency voltage source to a load in non-contact manner through a transformer with separable power and secondary windings.
2. Description of the Prior Art
The inventors disclosed "A Non-Contact Charger Using a Resonant Converter with Parallel Capacitor of the Secondary Coil" in a paper at pages 136 to 141, volume 1 presented at "Thirteenth Annual Applied Power Electronic Conference and Exposition (APEC '98)" on Feb. 15-19, 1998 at The Disneyland Hotel, Anaheim, Calif., U.S.A. The paper describes a charger system which is composed of a charger circuit including a power supply of providing a high frequency voltage across a power winding, and a load circuit for charging a rechargeable battery. The load circuit comprises a secondary winding, a matching capacitor, and a rectifier. The secondary winding, which is separable from the power winding, is magnetically coupled to the power winding so as to generate an induced high frequency voltage and to provide a leakage inductance to the load circuit. The matching capacitor is connected across the secondary winding to be cooperative with the leakage inductance and with the secondary winding to form an oscillatory circuit which provides an oscillating voltage across the matching capacitor for generating a supply current being fed through the rectifier to the battery. The matching capacitor is selected to have a specific capacitance such that the oscillating voltage reaches its minimum at a timing of the induced high frequency voltage going positive from negative. The inventors discovered that the selection of the above specific capacitance for the matching capacitor is responsible for giving a maximum charging current to the rechargeable battery and such capacitance is far from that calculated based upon a known concept of tuning the frequency of the high frequency voltage supplied from the power circuit to a resonant frequency of a resonant circuit composed of the matching capacitor and the secondary winding, as disclosed in Japanese Patent Early Publication (KOKAI) No. 6-178464.
However, since the above system is designed to provide a supply current in the form of a pulse to the rechargeable battery, it is likely to bring about a noise due to the discontinuity of the supply current. Also because of that the supply current having a relatively large peak flows through the secondary winding and a diode rectifier, there may be a considerable loss in these elements. Thus, the above system is found to be applicable only to the system of providing relatively small supply current where the loss is not critical. Therefore, it has been desired to accomplish a like system capable of providing a relatively large supply current of substantially uniform level, yet with an optimum transmission efficiency.